driving home last night I went over a sleeping policeman a bit too fast but no more than 30 mph ( I was distracted) subsequently I cannot select 5th gear. all others select though now a little stiff. I have checked and unshipped all the linkages and rods etc (they are all free moving). using the operating rod on top of the gearbox I can select by hand all gears except 5th. I have checked under the car and there is no visible damage as I said it wasn't that fast. Any ideas? as I am stumped and can only surmise that I have broken/bent something inside the box